Synergistic effects of fly ash on thermal, combustion, and mechanical properties of polypropylene including intumescent flame retardant

In this study, a fly ash (FA), primarily composed of SiO2, Al2O3, Fe2O3, MgO, and CaO, as a synergistic additive (1-5 wt%) was added to enhance the effectiveness of an intumescent flame retardant (IFR) system (25 wt%) in polypropylene (PP). The composites were characterized by various tests to study thermal, combustion, and mechanical properties. Experimental results revealed that both IFR and IFR/FA additions led to early degradation at lower rates, with increased residual mass values. The thermal conductivity coefficient increased up to 16.9% with IFR/FA additions. While the sample containing only IFR met the UL 94 V-0 requirements with a limiting oxygen index (LOI) value of 30.0%, the addition of 1% and 2% FA satisfied the UL 94 V-0 criteria with the LOI values of 32.8% and 34.9%, respectively. Cone calorimeter results indicated that IFR had significant positive impacts on the burning characteristics of PP. Furthermore, the incorporation of FA reinforced the char layer formed by IFR, thereby enhancing the fire resistances of the composites. Although the tensile strength and tensile modulus decreased with IFR addition, the Izod impact strength increased. Additionally, FA additions slightly improved the mechanical properties of PP/IFR composites. Characterization of polypropylene based composite materials including fly ash/intumescent flame retardant.image